The invention relates to a toroidal variable-speed drive unit.
DE 101 22 176 A1 discloses such a toroidal variable-speed drive unit. This toroidal variable-speed drive unit is arranged within the transmission case of a motor vehicle transmission and has two toroidal chambers, each with two rollers. The torque is transmitted in a continuously variable manner by means of these rollers. Each of the two rollers is
fastened to a supporting journal,
rotatable about its own axis of rotation, and
supported fixedly in terms of rotation with respect to a pivot axis of the supporting journal which is perpendicular to its own axis of rotation.
The two supporting journals form, in diagrammatic terms, the two lateral lines of a parallelogram. The upper and the lower line of the parallelogram are formed by two rockers, the central bearing receptacle of which is supported with respect to the transmission case. An axial force can be introduced into the supporting journals by means of actuating members, so that the angles of the parallelogram change. The angular movement of the parallelogram is in this case made technically possible in that the two rockers receive the supporting journals by means of articulated pivot bearings which allow a slight angular movement.
DE 199 47 851 A1 also discloses a toroidal variable-speed drive unit.
An object of the invention is to provide a cost-effective and nevertheless highly fail-safe toroidal variable-speed drive unit.
The high fail-safety is achieved advantageously in that, in addition to the “force synchronization,” typical of toroidal transmissions, which constantly holds all the rollers in the correct pivot-angle position during the operation of the toroidal variable-speed drive unit, “path synchronization” ensures operation. In this “path synchronization,” according to the invention, the supporting journals are received only with one side in a rocker. By contrast, on their other side, the supporting journals are supported with respect to the transmission case or to a component connected firmly to the transmission case.
This “rocker-free” support of the supporting journals in a bearing receptacle which is fixed in terms of movement with respect to the transmission case is advantageously particularly cost-effective. Thus, the articulated ends of the supporting journals can be received directly in bearing bores or plain-bearing bushes in the transmission case. This is accompanied by the advantages of a reduction in the diversity of parts.
Furthermore, a supporting plate connected fixedly in terms of movement to the transmission case may be provided for receiving the bearing bores or plain-bearing bushes. As a result, in a particularly advantageous way, the transmission case may consist of light, but also soft light metal, whilst the high forces occurring when the toroidal variable high-speed drive unit is in operation are supported in the supporting plate made from steel or cast iron.
Additionally, an embodiment of the invention allows an optimum functioning of the toroidal variable high-speed drive unit, in that the friction to be overcome in order to pivot the supporting journal about its own pivot axis is kept low by means of a rolling bearing. In a particularly advantageous way, the coefficient of friction between a convex rolling-bearing outer ring of this rolling bearing and a linear plain bearing may be designed in such a way that, in the case of an unchanged transmission ratio of the toroidal variable high-speed drive unit, the static-friction limit is not exceeded over a period of time, so that there are also no translational axial fluctuations of the supporting journal. By contrast, when a transmission ratio adjustment of the toroidal variable-speed drive unit, that is to say an axial displacement of the supporting journal, is specifically initiated, the static friction is exceeded and, because of the low sliding friction in the linear plain bearing, scarcely any wear occurs.
In an embodiment of the invention, in addition to “force synchronization” and to “path synchronization,” what may be referred to as “angle synchronization” ensures to a particular extent that the rollers of the toroidal variable-speed drive unit are in the correct pivot-angle position in relation to one another. This “angle synchronization” ensures the correct pivot-angle position of the rollers in relation to one another even when the toroidal variable-speed drive unit is not in operation and the rollers are nevertheless shaken about. This situation arises, for example, when the motor vehicle is towed away or is transported on a railway wagon.
In general, one advantage of power-split motor vehicle transmissions with a toroidal variable-speed drive unit is that, as a result of the use of a power path with a constant step-up, the toroidal variable-speed drive unit is relieved within wide operating ranges. This relief is advantageous particularly in the case of high-torque engines, in which the power take-off torque of the engine is markedly above the maximum permissible input torque of the toroidal variable-speed drive unit and therefore a reduction in the torque of the variable-speed drive unit solely by the preselection of a step-up stage into high speed would not be sufficient. The said high-torque engines are conventionally installed longitudinally in drive trains.
Moreover, along with the corresponding design of the motor vehicle transmission, the relief of the toroidal variable-speed drive unit gives rise advantageously to an improvement in the overall efficiency of the motor vehicle transmission in the corresponding driving range, since the power in the power path having a constant step-up can be transmitted with higher efficiency than in that having a continuously variable step-up.
A further advantage of the relief of the toroidal variable-speed drive unit is that the pressure forces at the driving/driven discs can thereby be lowered, thus leading to a lowering of the frictional losses. As a result of the reduction in the frictional losses, less heat also has to be discharged.
Furthermore, by the toroidal variable-speed drive unit being relieved, its useful life can be increased in an advantageous way.
One advantage of apportioning the transmission step-up to at least two driving ranges is that the spread of the motor vehicle transmission is increased.
Transmission spreads which are greater than the spread of the toroidal variable-speed drive unit thus become possible.
Both driving ranges can advantageously be implemented in the power-split mode, in order to increase the efficiency.
By means of a geared-neutral function, there is advantageously no need for a starting element, such as, for example, a hydrodynamic torque converter. The implementation of a geared-neutral mode makes it possible to have operation in which the driving states forward travel, reverse travel and standstill can be achieved solely by the adjustment of the toroidal variable-speed drive unit. Furthermore, there is no need for a reversing unit, such as, for example, a turning set with associated clutches or brakes, which likewise has an advantageous effect on weight, construction space and costs.
The motor vehicle transmission is used in a particularly advantageous way in a drive train with a front engine and a rear-axle drive. Furthermore, the motor vehicle transmission is used in a particularly advantageous way in an all-wheel drive which emanates from a modified drive train with a front engine and with a rear-axle drive. Such a drive train is shown in DE 101 33 118.5 which has not already been published.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.